1. Field of the Invention
The present invention relates to a shift device with a synchronizer for a transmission in which pressing force applied to a shift sleeve can be amplified into larger pressing force acting on a synchronizer ring while gears of the transmission are shifted, thereby reducing operating force necessary for a driver or an actuator.
2. Description of the Related Art
A shift device with a synchronizer for a transmission of this kind is disclosed in Japanese examined patent applications publication No. 2007-040491 and No. 2007-225071. These conventional shift devices have a hub, a sleeve, synchronizer rings and a plurality of thrust pieces. In these shift devices, contact of slopes between the hub and the synchronizer ring changes friction torque generated by the synchronizer ring into thrust for pressing the synchronizer ring, thereby amplifying press force acting on the synchronizer ring to increase synchronization performance. This is called as a self-servo effect or force amplifying effect.
The thrust pieces are provided between the hub and the synchronizer ring so that they can swing in cut-off portions of the hub to obtain the force amplifying effect by contacting the slopes of the thrust pieces and the hub. The thrust pieces prevents the slopes from being contacted with each other when the sleeve is positioned at a neutral position in order to remove the thrust due to drag friction torque of the synchronizer ring at the neutral position.
These conventional shift devices with the synchronizer, however, encounter the following problems.
In order to ensure the thrust pieces to swing in the cut-off portions in theses conventional shift devices, the cut-off portions of the hub need a sufficient axial length to some extent. This makes it difficult to apply the thrust pieces to a shift device for a reverse gear, because a hub of the reverse-gear shift device is formed together with a gear as one unit and is formed with splines, an axial length of which becomes short.
It is, therefore, an object of the present invention to provide a shift device with a synchronizer for a transmission which overcomes the foregoing drawbacks and can apply swingable thrust pieces to a shift device, having a hub with splines in short axial length, such as a reverse-gear shift device.